Multicone exhaust diffuser system for a gas turbine

ABSTRACT

An exhaust system for hot motive fluid gases expelled from a gas turbine wherein the hot gases pass into an annular chamber, thereafter the gases are directed through a circumferential array of transition members. Each transition member directs the exhaust gases through generally axially directed diffuser cones. The downstream bearing, the bearing support members and the last row of blades in the gas turbine, are easily accessible because the exhaust cones direct the hot exhaust gases away from those areas.

United States Patent 1 Hugoson et al.

MULTICONE EXHAUST DIFFUSER SYSTEM FOR A GAS TURBINE Inventors: Birger O.Hugoson, Wallingford;

Carl A. Rohr, Springfield, both of Pa.

Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

Filed: Jan. 16, 1974 Appl. No.: 433,960

US. Cl 60/3931; 60/3932; 415/219 R Int. Cl. F02C 7/20; F01D 25/24 Fieldof Search 60/3932, 39.5, 39.31;

415/201, 209, 219 R, 139; 181/33 H, 33 HB, 33 HD, 41, 46; 239/265.25,265.27

References Cited UNITED STATES PATENTS Buckland et a1 416/171 Dec. 23,1975 2,922,278 1/1960 Szydlowski 60/3936 2,933,893 4/1960 Blyth etal.... 3,448,825 6/1969 Booth 181/33 HB Primary Examiner-G. J. HusarAssistant Examiner-Thomas 1. Ross Attorney, Agent, or Firm--F. A. Winans[57] ABSTRACT 5 Claims, 3 Drawing Figures US. Patent Dec. 23, 1975 Sheet1 of2 3,927,521

US. Patent Dec. 23, 1975 Sheet 2 0f 2 BACKGROUND OF THE INVENTION 1.Field of the Invention:

This invention relates generally to gas turbines and more particularlyto exhaust systems for gas turbines.

2. Description of the Prior Art:

As is well known in the art, low pressure ends of axial flow elasticfluid turbines are usually provided with a diffuser for directing fluiddischarged from the last stage turbine blades along a smooth aerodynamicpath to the ambient atmosphere, as in the case of gas turbines.Diffusers for large stationary gas turbines are often formed fromradially spaced inner and outer fairing members forming an annularshapedexhaust outlet for the discharged fluid. The downstream axis supportbearing is disposed within the inner fairing member, andaerodynamically-shaped bearing support struts are disposed acrossthe hotexhaust gas annular flow path between the two fairing members. Thehearing support struts also, however, create a turbulent flow of exhaustgas, thereby reducing the efficiency of the diffuser in its ability toconvert the kinetic energy of the moving fluid into pressure. Thedischarged fluid does not move smoothly into the exhaust section of theturbine, with major consequences being a decrease in overall turbineefficiency. The downstream support bearings, within the inner fairingmemberis disposed within an area that is difficult to reach and hencedifficult to inspect without major dismantling of the exhaust system.

In addition to hampering serviceability, present design calls for theuse of bearing support strut members being disposed across the hot gasflow path and through site of the purchaser. This places restrictions onthe allowable shippable dimensions of the turbine member itself.

An object of the present invention is to overcome the problems presentedabove in the prior art.

Anotherobject of the present invention is to permit the shipping of aslarge a gas turbine as practically possible with minimum field assembly.

A still further object of the present invention is to provide an exhaustsystem for a gas turbine that will permit access to the downstreamsupport bearing.

Yet another object of the present invention is to provide an exhaustsystem for a gas turbine having a minimum decrease in turbine efficiencydue to the turbine exhaust gas diffuser.

SUMMARY OF THE INVENTION A system for ducting hot exhaust gases from agas turbine is provided wherein the downstream bearing, shaft and laststage blades are accessible for service. In this system, the exhaustgases, after passing through the last stage blades, enter an annularchamber. From this chamber, the exhaust gases pass through transitionmembers into conically-shaped ducts or diffusers which are inregistration with the transition members and the annular chamber. Theconical diffusers have their in creasing diameters in the generallyaxially rearward direction.

Bearing support struts are disposed between the diffusers. This avoidsthe need for the support struts being disposed through the hot exhaustfluid flow area, which would decrease the overall turbine efficiency.The arrangement also reduces the allowable transport or shipping size ofthe turbine, and reduce the downstream bearing, shaft and last stageblade accessibility.

Other details and advantages of this invention will become'apparent asthe following description of a present preferred embodiment proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the exhaust end of a gasturbine with half of the exhaust system cut away;

FIG. 2 is a side view of an exhaust diffuser arrangement showing thedifferent zones therein; and

FIG. 3 shows an arrangement of a pair of exhaust hoods that connect tothe exit end of the diffuser cones.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings,particularly to FIG. 1, there is shown a portion of an axial flow gasturbine 10 including a rotatable shaft 12, a last stage rotor disc 14mounted on said shaft 12, a plurality of radially directed blades 16mounted on said disc 14, a bearing 18 supporting the downstream end ofsaid shaft 12, a plurality of elongated bearing support struts 20, andan exhaust diffuser arrangement 22. As is well known in the art, hotmotive gas fluid is supplied through the motive fluid flow passageway,comprised of the rotating and stationary blades, only the rotatingblades 16 of the last stage are shown. During flow past the blades, thehot motive gaseous fluid is expanded to impart rotational energy to therotor.

The gas turbine 10 in the illustration shown, is of the axial flow type,having a shell structure 24 and turbine support member 26. The hotmotive fluid is directed from the last row of blades 16 to an exhaustannulus 28, which is defined by a generally toroidal-shaped ring 30 onthe downstream end of the gas turbine 10. The toroidal-shaped ring 30has a plurality of transition members 31 attached adjacent orifices, notshown, in the toroidal-shaped ring 30. g

A plurality of diffuser cones 32, eight in this example, but only fourshown, are attached to the transition members 31 and hence inregistration with the toroidalshaped ring 30, which comprise the exhaustdiffuser arrangement 22. A dotted outline shown in FIG. 1 represents anexhaust hood member 37 which is part of the exhaust system. Across-section of the toroidalshaped ring 30 and a side view of thetransition member 31 and diffuser cone 32, that comprises an additionalportion of the exhaust fluid diffuser arrangement 22, is shown in FIG.2. Several zones are indicated therein. Zone A is called the annulardiffuser zone. The walls of zone A are curved so as to act to suppressseparation of the hot fluid exhaust gases. A portion of the energyconversion from kinetic energy into static pressure can be made in thehot exhaust gases before entering the next zone, called the transitionzone, and indicated by the letter B. A slight reduction incross-sectional area in the direction of the exhaust gas flow isintroduced on the toroidal ring 30 adjacent the transition member 31, tokeep the exhaust gas flow aligned. The velocity distribution of the hotexhaust gas flow is kept as uniform as possible as it enters the thirdzone called the conical diffuser zone, and indicated by the letter C.The transition member 31 and the exhaust diffuser cone 32 each have aflange, 33 and 34, at their juncture, to permit assembly thereby.

An exhaust hood arrangement 36 is shown in FIG. 3. The exhaust hoodarrangement 36 is comprised of at least two exhaust hood members 37 and37 The exit ends of the conical diffuser cones 32 mate with orifices 38in each exhaust hood member 37 and 37 The exhaust hoods 37 and 37,deflect and duct the hot fluid exhaust gases away from the turbine 10.,Tie bars 39 connect the exhaust hood members 37 and 37 to take thelateral forces generated therein by the turning of the hot gaseousexhaust fluid flow. Axial forces within the exhaust hood members 37 and37 are transmitted by other tie rods 41 back to the gas turbine supportmembers 26. Expansion joints 38 are provided at the junction of thediffuser cones 32 with the exhaust hood members 37 and 37. The exhausthood members 37 and 37' are each separate shippable members themselves,permitting simple field assembly.

Utilizing this exhaust arrangement, the exhaust diffuser cones areeasily removable for inspection and repair of the downstream bearing 18,the shaft 12 and the last stage blades 16. The turbine itself may beshipped to the field without the exhaust diffuser arrangement 22attached thereto. Prior art arrangements require complete assemblybefore shipment because the bearing support struts extend through theexhaust annulus. That is, it must be assembled prior to shipment forsupport of the bearing and shaft. This reduces the maximum size of theturbine shippable because of the overall dimensional limitation imposedby the shipping envelope.

While we have shown and described a present preferred embodiment of thisinvention, it is to be distinctly understood that the invention is notlimited thereto, thatthe invention may be otherwise variously embodiedwithin the scope of the following claims.

We claim:

1. In a gas turbine installation including: a housing, a shaft rotatablymounted in said housing by means including a downstream bearing,alternating annular arrays of stationary and rotatable blades, saidrotatable blades being attached to said shaft, a hot motive fluid flowpath within said housing, the hot motive fluids driving said rotatableblades, an inlet in said turbine for the hot motive fluid, and a hotmotive fluid exhaust outlet arrangement for the hot motive fluid, saidhot motive fluid exhaust outlet arrangement comprising:

an annular chamber downstream of the last array of said rotatableblades,

a plurality of generally axially disposed transition members inregistration with said annular chamber,

an annular array of a plurality of tubular-shaped generally axiallydirected hot motive fluid exhaust ducts, each in fluid communicationwith one of said transition members, said ducts being generallycomprised of truncated diffuser cones, the smaller diameter of saidtruncated cones mating with said transition members,

a plurality of downstream bearing support members disposed betweenadjacent exhaust ducts, said bearing support members extending betweensaid bearing and said housing,

said hot motive fluid exhaust ducts being detachable from saidtransition members, to permit access to the bearing and bladeassemblies, said bearing support members being free from contact withthe hot motive fluid exhaust to limit any thermal effects therein,

a pair of exhaust hoods attached to the downstream ends of said diffusercones with an expansion joint therebetween, each of said exhaust hoodsdirecting the flow of the hot motive fluid exhaust away from the gasturbine, each of said exhaust hoods having an array of half of saidplurality of diffuser cones attached thereto.

2. A gas turbine installation as recited in claim 1, wherein saiddownstream bearing is disposed axially beyond said annular chamber, saiddownstreambearing being generally in contact with the ambient air.

3. A gas turbine installation as recited in claim 1, wherein saidtruncated diffuser cones have flange portions which attach to flangeportions of said transition members.

4. A gas turbine arrangement as recited in claim 1, wherein tie barsconnect the two exhaust hoods together to restrain the lateral forcesgenerated by the turning of the flow of exhaust gases.

5. A gas turbine installation as recited in claim 1, wherein a pluralityof tie bars transmit axial forces generated within the exhaust hoods tothe gas turbine housing.

1. In a gas turbine installation including: a housing, a shaft rotatablymounted in said housing by means including a downstream bearing,alternating annular arrays of stationary and rotatable blades, saidrotatable blades being attached to said shaft, a hot motive fluid flowpath within said housing, the hot motive fluids driving said rotatableblades, an inlet in said turbine for the hot motive fluid, and a hotmotive fluid exhaust outlet arrangement for the hot motive fluid, saidhot motive fluid exhaust outlet arrangement comprising: an annularchamber downstream of the last array of said rotatable blades, aplurality of generally axially disposed transition members inregistration with said annular chamber, an annular array of a pluralityof tubular-shaped generally axially directed hot motive fluid exhaustducts, each in fluid communication with one of said transition members,said ducts being generally comprised of truncated diffuser cones, thesmaller diameter of said truncated cones mating with said transitionmembers, a plurality of downstream bearing support members disposedbetween adjacent exhaust ducts, said bearing support members extendingbetween said bearing and said housing, said hot motive fluid exhaustducts being detachable from said transition members, to permit access tothe bearing and blade assemblies, said bearing support members beingfree from contact with the hot motive fluid exhaust to limit any thermaleffects therein, a pair of exhaust hoods attached to the downstream endsof said diffuser cones with an expansion joint therebetween, each ofsaid exhaust hoods directing the flow of the hot motive fluid exhaustaway from the gas turbine, each of said exhaust hoods having an array ofhalf of said plurality of diffuser cones attached thereto.
 2. A gasturbine installation as recited in claim 1, wherein said downstreambearing is disposed axially beyond said annular chamber, said downstreambearing being generally in contact with the ambient air.
 3. A gasturbine installation as recited in claim 1, wherein said truncateddiffuser cones have flange portions which attach to flange portions ofsaid transition members.
 4. A gas turbine arrangement as recited inclaim 1, wherein tie bars connect the two exhaust hoods together torestrain the lateral forcEs generated by the turning of the flow ofexhaust gases.
 5. A gas turbine installation as recited in claim 1,wherein a plurality of tie bars transmit axial forces generated withinthe exhaust hoods to the gas turbine housing.